Unsaturated compounds, particularly vinyl monomers, can undesirably polymerize at various stages of their manufacture, processing, handling, storage, and use. Vinyl monomers can undergo self-initiated polymerization at elevated temperatures even in the absence of polymerization promoters. Thus, undesired thermal polymerization can be a problem during the purification of vinylic monomers and during sudden process shutdowns. Undesirable polymerization results in product loss because the valuable monomer end product is consumed in an undesired side reaction. Moreover, unwanted polymerization results in the precipitation and deposition of polymer foulants on the process equipment thereby reducing production efficiency. Unless the unwanted polymerization is effectively controlled, this fouling of process equipment may require a shutdown of the process so as to remove the undesired polymer by physical methods. This problem is particularly acute in the manufacture and purification of vinyl aromatic monomers.
To prevent the formation of unwanted polymer as well as protecting the process equipment, the dominant products in current use are efficacious and low-cost dinitrophenols (DNP). A prototype of DNP antipolymerants in the market is 2,4-dinitro-sec-butylphenol (DNBP). It is a highly effective antipolymerant. However, DNBP is very toxic and a known environmental hazard such that is becoming highly regulated, with the ultimate objective of completely eliminating the usage of said antipolymerant. A prime example is Europe's REACH legislation. Another equally significant disadvantage is that the DNP compounds release NOx emissions during incineration. As a consequence of these disadvantages, there is a need for antipolymerant compounds that are as efficient as DNBP at reducing polymerization and yet are safe and environmentally friendly.